A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. A FBG can be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector. FBG sensors, which are a type of fiber optic sensors, are currently used as direct sensing elements for strain and temperature in applications such as seismology, pressure sensors for harsh environments, and sensors in oil and gas wells.
Perimeter protection and intrusion detection systems (PIDS) and methods have become an essential part of most security and surveillance systems. From applications such as border protection, airport security, equipment protection in plants, etc, PIDS have penetrated a large number of fields. The core detection technologies that are currently used in PIDS systems include microphonic sensors, microwave sensors, seismic, sensors; and they have been the traditional solutions. Lately, optical fiber-based PIDS have gained popularity, being a fully passive system and not requiring power supplies or electronics in the field. In addition, there is always a demand from the market to make PIDS solutions more robust and foolproof, especially in the protection of critical infrastructure and high security areas, where it is essential that advances to PIDS systems include more accurate measurements.
A brief description of the various types of fence-mounted PIDS is given below:
Co-axial Cables: These fence or buried sensors have powerful digital signal processors to detect minute flexing in the cables along the fence.
Fiber-optic Cables: These analyze disturbances or light deflections within the fiber-optic cable caused by cutting, flexing, sawing or climbing the fence.
Microphonic Sensors: Coaxial or magnetic type sensors detect sounds associated with cutting, flexing, sawing or climbing the fence.
Taut-wire: These sensors detect changes to the tension on the fence.
Vibration: Cables are attached to one of more sensor devices which sense vibrations resulting from cutting, flexing, sawing or climbing.
However, current PIDS are susceptible to false alarms. For example, nuisance events such as rain, birds sitting on a fence or seismic vibrations caused by aircraft landing or taking off may raise false alarms.
A need therefore exists to provide a fiber Bragg grating (FBG) sensor structure, a method of fabricating the same, and a method of employing the same that seeks to address at least one of the abovementioned problems.